30 GEOLOGICAL, MEMOIRS. 



jected to a general classification. The group of the Bernina, with 

 its gneiss and mica-slate, forms the central mass, occupying all the 

 space between Oher-Engadin and the Val Camonica, the serpen- 

 tines of Val Malenco, and the limestones of Ortles. It is remarkable 

 for the height of its peaks, the beauty of its glaciers and snow- 

 fields, and the crystalline constitution of its rocks. Nowhere in these 

 districts does the gneiss appear in such force, and the ice -mountains 

 which reach to the Bernina road are among the most considerable 

 which the Alps exhibit. Unlike all the '^central masses" described, 

 the Bernina is almost completely surrounded by a circle of granite, 

 hornblende rock, and serpentine. One might well be tempted to re- 

 cognize in this mass the lever that has here elevated the gneiss to 

 so unusual a height. The main road over the Bernina leads from 

 the heights round the lakes more to the eastward, past the Motta and 

 the Mont Rosa. On the north bank of the Lago Bianco a dark-green 

 rock resembling serpentine prevails ; and gneiss on the steep declivity 

 towards the ravine of the Motta and the descent to Mont Rosa. The 

 granite of Mont Brusio only appears in the form of a considerable 

 bed. 



The nucleus of the Selvretta in many points reminds the observer 

 of the '* central mass " on the exterior margin of the middle zone : 

 in other respects it has its own peculiar characters, like each of the 

 other groups. A fan-like structure is observable ; the alpine granite 

 forming the axis of the fan, the crystalline slates stretching over the 

 limestone rocks, &c. On the other hand, the gneiss over a great 

 part of the group is replaced by a great development of hornblende 

 slate. Passing over Fluella we have an excellent view of the relations 

 of the western fan-shaped rocks. 



Finally, the mass of the Oetzthal Ferner resembles that of Sel- 

 vretta : gneiss and mica-slate penetrate like wedges into the Biindtiier 

 Alps. . In the loftiest southern portion two fan-like series of mica- 

 slate can be recognized. 



This general description of the mountains is followed by a more or 

 less detailed account of the various rocks which compose them ; — 

 granite, hornblende rock, serpentine and gabbro, green slate, grey 

 slate, limestone and marble, dolomite, gypsum, verrucano, quartzite, 

 and red sandstone: their occurrence in each particular spot is enu- 

 merated, and their characters described. We shall quote one or two 

 of these observations. 



With regard to serpentine and gabbro, it is said, — the question 

 is not yet settled whether serpentine, and the gabbro which fre- 

 quently accompanies it, are to be looked on as plutonic masses, which 

 have caused the protruded rocks to pass into grey and green slates ; 

 or whether they are to be regarded as the last stages of the meta- 

 morphosis of the slates. The author is of opinion that unprejudiced 

 judgments will give the preference to the latter hypothesis ; though 

 he candidly admits that it is open to more objections than the 

 former. 



We have often taken occasion to speak on the doctrine of meta- 

 morphism, so popular of late years. Far from being opposed to geo- 

 logic transformations, we are of opinion that within certain limits 



